This invention relates to an image reading apparatus for scanning and optically reading a document image and outputting electronic data. More particularly, this invention relates to a structure of an automatic document feeder for transporting documents to a determined reading station and for discharging documents.
Image reading apparatus optically read images on a document, convert the images to electronic data, and transmit that data to image forming apparatus, such as an external personal computer, a copier or a facsimile machine. Many image forming apparatus are equipped with such image reading apparatus.
Image reading apparatus are provided with a light source for irradiating light onto a document that is pulled out and transported by an automatic document feeder one at a time and image sensors that receive the light reflected from the surface of the document.
However, it has been demanded recently that the automatic document feeder apparatus disposed on image reading apparatus be compact, lightweight and comprise fewer parts. Such an improved apparatus disclosed in Japanese Patent Publication 62-179271 shows a structure that has discharge rollers immediately after the document reading station so that these discharge rollers discharge documents to a discharge tray. This apparatus shortens the path to transport documents, and due to a configuration using least minimum number of rollers required in the transport of the documents, the structure for the transport of documents can be compact, lightweight and has fewer parts.
This apparatus is provided with a detection means to detect documents between a reading position for reading documents and discharge rollers. In general, there are two types of detection means; a lever type sensor detection method (or a lever type sensor) detects a motion of a detection lever disposed in the transport path swung by a sheet of document; and a reflective type sensor detection method (or a reflective type sensor) detects an interruption of light caused by a sheet of document. The light is emitted from a light-emitting unit, and is configured to be reflected by a reflective plate and returned to a light reception unit.
However, when employing the former lever type detection method, having a detection means between the document reading station and the discharge roller causes a problem, where a shock of the document striking the lever distorts images while being read because the documents is in a free state when the edge of the document hits the lever.
In particular, when the image sensor is a contact image sensor (CIS) type using a SELFOC lens, not only distortion of the image but out-focus can occur since the focus depth of CIS type sensor is extremely shallow compared to a reduction type sensor.
Also, when the latter reflective type sensor is employed, the light generated by the light source for the reading means can be mistakenly detected.
Particularly, if the image sensor is a reduction type for reading images via a plurality of mirrors reflected from a document surface, there is a greater chance of such error due to higher intensity of light.
An object of the present invention is to provide a document reading apparatus that it will not create a shock to documents while being read even though a reading apparatus is compact and lightweight. Another object of the present invention is to provide a document image reading apparatus that prevents a detection error during document transportation and achieves reliable detection.
This invention comprises a transport path for sequentially feeding documents from a sheet supply tray, a reading station for reading images on the documents disposed in the transport path, a photoelectric conversion means for photo-electrically converting images on documents moving over the reading station, a discharge tray for storing documents coming from the reading station, a first transport roller disposed at a front position in the transport direction of the reading station, a second discharge roller disposed at a back position in the transport direction of the reading station, a first detection means arranged upstream of the transport roller and a second detection means arranged at a position on the discharge tray side from the point at which the second paired transport rollers contact each other.
Furthermore, the second detection means has a stick-shaped lever member hanging downward that is capable of being swung by an edge of document abutting thereon at a position on the side of the discharge tray from the point at which the second transport rollers contact each other.